Although many contingency situations involve the use of distinct behaviors as instrumental and contingent events, contingencies involving only one moderately probable behavioral event (intra-behavioral contingencies) are frequently encountered in an organism's natural environment. In the typical intra-behavioral contingency, the time spent engaged in a behavior (or the time spent between instances of the behavior) is controlled by the subject, but when a time-criterion is violated during this voluntary behavior, the duration of the following wait between instances of the behavior (or the duration of the following instance of the behavior) is removed from the subject's control. Thus, the instrumental event consists of forced curtailment of the wait (or behavior) or forced continuance of the wait (or behavior). For the most part, intra-behavioral contingencies have been ignored in studies of reinforcement and punishment. As a result it is not known whether or not intra-behavioral contingencies are effective, or--if they are effective--whether they bring about the changes in behavior typically expected by the individual arranging the contingency. The proposed study is an extension of preliminary work on one form of intra-behavioral contingency and preliminary work on another form. Forced running in rats will be used in both studies. In the extended study the effects of various contingent durations of forced running will be tested by systematically presenting different contingent durations to each subject.